Automatic sear release for firearms



c. w. RoBBlNs 2,427,304

AUTOMATIC SEAR RELEASE FOR FIREARMS Filed sept. so, 1942 l 5 sheets-Sheet 1 INV ENT OR CHARLES WILLIAM ROBBINS Sept. 9, 1947.

c. w. RoBBlNs 2,427,304 UTOMATIC SEAR RELEASE FOR FIREARMS Filed sept. 5o, 1942 5 sheets-sheet 2 Sept. 9, `V1'947.

Sept; 9, 1947. c. w. ROBBINS 2,427,304

AUTOMATIC: SEAR RELEASE For;v FIREARMS A Filed Sept. 50, 195212 5 Sheets-Sheet 3 @g |88 a@ nnnnvnak CHARLES WILLIAM Roams Sept 9, 19475- c. w. RoBBlNs 2,427,3041

AUTOMATIC SEAR RELEASE FOR FIREARMS Y Filed sept.l 30, 1942 5 sheets-Sheet 4 INVENTOR. CHARLES w|LL|AM RoBsms Sept. 9, 1947.

c. w, RoBBlNs AUTOMATIC SEAR RELEASE FOR FIREARMS 5 Sheets-Shet 5 Filed Sept. 30, 1942 FIG. I9

' INVENTOR l CHARLES WILLIAM noaams BY Patented Sept. 9, 1947 4 Claims.

The present invention relates to firearms, and more particularly to rearms of the so-called sub-machine gun type which are used by many, if not all of the up-to-date law enforcing agencies. These guns are usually of .45 calibre or larger, and are adapted to be red at cyclic rates up to 800 shots per minute when operated full automatic.

In order that those persons whose duty it is to operate sub-machine guns may be adept at handling such Weapons in times of emergency, it becomes imperative that such persons practice at frequent intervals for the purpose of mastering the characteristics of such guns, especially when CTI means described herein and disclosed in the accompanying drawings, in which:

Fig. 1 is a vertical central longitudinal section through a .45 calibre sub-machine gun of the Thompson type, showing one form of my ,22 calibre adapter mechanism associated therewith, certain parts being shown in elevation for clarity of detail.

Fig. 2 is a vertical section through a large calibre sub-machine gun showing another form of .22 calibre adapter mechanism of the present invention, with the parts shown in red position.

Fig. 3 is similar to Fig. 2, showing the parts in complete recoil and cocking position.

fired full automatic. Unfortunately, practice pel5 Fig. 4 is similar to Fig. 2, showing the parts in riods, at most law enforcing agencies are not as the primary cartridge stripping position immedifrequent as desirable, rst, because of the high ately after the trigger had been pulled.

cost of .45 calibre ammunition, and secondly, be'- Fig. 5 is a side elevational view of a modified cause of the danger inherent when iring such form of the adapter mechanism of Fig. 1 with the ammunition. bolt in a fully extended position.

The primary object of the present invention Fig. 6 is a top elevational view of the device of is to provide means for converting a .45 calibre Fig, 5. sub-machine gun for use with and operation on Fig. '7 is a perspective view of the bolt and r- .22 calibre ammunition without sacrificing the ing pin which form a detail of the adapter mechmajor recoil and muzzle blast characteristics 2b anism disclosed in Figs. 5 and 6. which are inherent with the use of .45 calibre Fig. 8 is a side elevational view of the firing ammunition. pin release mechanism of the adapter of Figs. 5

Another object of the invention is to provide and 6.

a .22 calibre conversion unit which is adapted to Fig. 9 is a sectional View taken on line 9-9 of be quickly and easily nterchanged with the'r- 30 Fig. 6 showing the relationship of parts when the ing mechanism of a larger calibre sub-machine firing pin release mechanism is in a firing pin regun. taining position.

Still another object of the invention is to pro- Fig. 10 is similar to Fig. 9 showing the relavide simple, yet durable mechanical means for tionship of the parts incident to tripping of the enabling a large calibre sub-machine gun to be firing pin release mechanism. red single shot or full automatic on small cali- Fig, 11 is a top elevational view of a modified bre, inexpensive ammunition. form of adapter mechanism, comprising a detail A further object of the invention is to provide of the present invention. means for exaggerating and multiplying the re- Fig. 12 is a perspective view of the bolt and coil incident to the ring of a .22 calibre cartridge iiring pin of the adapter disclosed in Fig. 1l. so as to approach` the recoil produced incident Fig. 13 is a sectional view taken on line l-i to the ring of a larger calibre cartridge. of Fig, l1 showing the rotary bolt actuated r- Another object of the invention is to provide ing pin lock in a Afiring pin retaining position. simple, yet highly effective means for automati- Fig. 14 is a sectional View similar to Fig. 13 cally feeding .22 calibre ammunition to the herebut showing the ring pin lock in a iiring pin inabove referred to conversion unit whereby the release position. gun may be operated full automatic. Fig. 15 is a sectional View of an insert barrel Still another object of the invention is to proadapter comprising a detail of the invention. vide a conversion unit and a cartridge feeding Fig. 16 is a sectional View of a gas expansion device of the character hereinabove described, nozzle which comprises a detail of the invention.

each of which are adapted to be operatively secured to the frame of a sub-machine gun without requiring the use of special tools or auxiliary holding devices.

These and other objects are attained .by the Fig. 17 is a side view of a cartridge magazine, partially in section, which comprises a detail of the invention.

Fig. 18 is a rear elevational View of the device of Fig. 17, but with the cartridges removed.

agradece Fig. 19 is a top elevational view of the device of Fig. 18.

Fig. 20 is a sectional view taken on line 22i of Fig. 17 showing the relationship of a recoiling bolt relative to the uppermost cartridge and the magazine lingers.

In Fig. l, a Thompson sub-machine gun is shown wherein the regidar, or standard .45 calibre bolt (including the firing pin, hammer, extractor .and hammer pin), actuator and recoil spring have been removed and replaced by my .22 calibre adapter.

As best disclosed in Figs, 2-4 inclusive, the ,22 calibre adapter comprises, broadly speaking, the following elements: an insert barrel 35i, a bolt block 3i, lock frame 32, recoil spring 33 for bolt block S l, hammer 3S, hammer pin 37, hammer spring 33, hammer spring guide 3g, combination spacer block and spring guide 35, scar and a .22 calibre cartridge magazine lit.

Insert barrel 38 may be bodily introduced into the regular barrel t1 of the gun from the rear or breech end. The insert barrel may include a rifled portion an enlarged bolt receiving portion or firing chamber i9 and an enlarged abutment 5o which is adapted to engage face Patil oi the standard or large calibre iiring chamber provided in the gun receiver 5d thereby locating the insert barrel relative to the regular barrel lill. It will be observed that the forward end El of the insert barrel terminates short of the end of the regular barrel by a dimension indicated by the letter X. The insert barrel may be held in place by engagement with a spacer block 53 secured to and carried by the forward end of lock frame 32 which lock frame is adapted to be inserted upwardly into the receiver 5t and then pushed forward until corresponding mating members on the insert barrel abutment El@ and the lock frame block 53 engage one another. When such an engagement has been effected, the insert barrel has been properly and automatically aligned relative to regular barrel Gl.

The lool; frame 32, which comprises a pair of laterally spaced side plates 320 interconnected at their forward ends by spacer block 53 may be held in place against the forward wall 55 of the receiver by means of a spacer block 'S5 formed of any suitable material adapted to withstand the shock of recoil which occurs incident to firing of the gun. 1f desireds the spacer block 35 may be provided with a pair of spring receptive chambers 5B and 5l for aligning recoil spring 33 and hammer spring 38 relative to bolt Si and hammer 36 respectively whereby the springs will normally urge the bolt and hammer forwardly, that is, to the right, toward front wall 55 of the receiver. At this point it should be observed that no special tools are required when inserting my adapter device into the receiver of a large calibre sub-machine gun. After the .22 calibre adapter has thus been located in the receiver, the gun frame 53 may be secured in place thereby fastening the lock frame 32 and spacer block 35 within receiver 5.

With particular reference now to Figs. 2, 3 and 4, it will be observed that bolt block 3l comprises a forwardly extending bolt portion 5S, a rearwardly extending portion til, and an intermediate portion 5l disposed at substantially right angles to portions 59 and Sil. The upper end of intermediate portion [il maybe provided with and terminate in a cooking knob 62. The lower face of the bolt 59 is preferably cut away as at @3 whereby to provide a stripping lug l2 which is adapted to engage the upper rear edge of the rim 65 of a cartridge 6d positioned between the upstanding fingers of cartridge magazine 6.

The hammer pin d? extends through a hole 63 in bolt 59, said hammer pin adapted for reciprocatory movement relative to the bolt. The opposite end of the hammer pin terminates at and is secured to hammer 36, by any convenient means. In the adapter unit disclosed in Figs. 2, 3 and l, hammer 35 is provided with a sear lug 39 having an upright face l@ and an inclined face Tl, as illustrated. Sear i5 may be pivotally mounted to a side wall 32d of the lock frame 32 by means of a pivot pin l2. The sear comprises a short upper leg 'i3 and a longer lower leg lli, the free end of the upper leg being provided with a sear lug engaging face 'l5 and the free end of lower leg is provided with a bolt lug engaging face le, which is adapted to engage bolt lug d6 which is carried by and secured to the rear end oi portion Lili of bolt block 3i. Sear l5 is normally urged in a clockwise direction about pivot pin l2 by means of a suitable spring member such as W which may be mounted on pins 'HS and iS carried by a side wall of the lock frame. The free outer end 8d of the Spring is adapted 'to engage notch 3i of the sear.

It should be understood that the scar is fixed relative to lock frame 32, whereas the bolt block 3i and hammer Se are adapted for reciprocatory movement relative to the sear and lock frame.

With reference now to Fig. 3, it will be observed that iace l5 of upper sear leg "i3 is adapted to engage upright face Hi of sear lug 69 of the hammer 38, thereby restraining the hammer against forward movement, to the right, in response to the action of spring 38, for maintaining the hammer in a fully cocked position. t will be observed that when the bolt block 3l has been moved rearwardly against spring 33 to a full retracted position, member Btl of the bolt block extends under and to the rear of the sear, and the bolt lug 65 is spaced from and to the rear of face l of lower leg M of the scar.

The hammer is adapted to be release-d or tripped from the cocked position disclosed in Fig. 3 when bolt lug 65 strikes face 'it of lower leg 'te of the scar as the bo-lt block Si is moved forwardly, to the right, by spring 33. rIhe impact imparted toy the sear by the bolt lug 5S moves the seal' in a counterclockwise direction about pivot pin i2 and against the counteraction of spring 'il for disengaging face 'i5 of the sear from forward face 'id of Sear lug 59, thereby permitting the hammer to be shot forwardly, to the right, to the position disclosed in Fig. 2, under the influence of spring 38.

At this point it should be observed that bolt 5S is adapted to reciprocate within chamber 49 of the insert barrel 39, the forward limit of bolt travel relative to chamber lie being determined by shoulder `83, the rearward limit of bolt travel being determinedlby the characteristics of spring 33. With reference now to Fig; .3, it will be observed that when the bolt block has been fully retracted, cartridge 'ed is urged upwardly by means of mechanism housed within magazine 45, which will be described in detail later, to present cartridge rim or base 55 to be engaged by stripping lug t2' incident to forward movement, to the right, of the bolt. As the bolt moves to the right, cartridge Sil is stripped, or transferred from the magazine to firing chamber 49, whereby cartridge base 65 will be lodged between shoulder 83 of the insert barrel and forward face 24 of the boit. The physical relationship of the bolt, hammer, sear, and bolt lug are such that the hammer will be released from the full cocked position disclosed in Figs. 3 and 4 concurrently with, or a split second before, the bolt reaches the end of its forward travel for positioning the cartridge base 65 between the forward face 84 of the bolt and shoulder 83 of chamber 09, whereby the cartridge will be discharged at the proper moment. When the cartridge has been discharged its projectile 86 will be shot forwardly, to the right, through rifled portion i8 of the barrel by the force of the expanding gas 81 generated incident to the firing of the powder charge of the cartridge. Gas 81 not only pushes the projectile forwardly through the barrel, to the iight, but it likewise acts upon cartridge case 85, pushing it rearwardly, to the left, against face 80 of bolt 59 with such force as to move the entire bolt block and hammer assembly rearwardly, to the left, against the counterforce of springs 33 and 38 for effecting a complete recoil of the bolt to the position disclosed in Fig. 3. The cartridge case 85 may be ejected by means of an ejector 88, which may, if desired, be mounted on magazine d5 as hereinafter more fully explained. The recoil of the bolt block and hammer assembly will continue after cartridge case 85 has been thus ejected from barrel chamber 49. As the bolt block and hammer assembly are thus moved rearwardly, to the left, short leg 13 of the sear will engage inclined face 1| of the sear lug for turning the sear in a counterclockwise direction incident to which face 15 of the sear will become engaged with face of sear lug 69 for establishing the relationship of ,parts disclosed inf. Fig. 3.

Unless the regular gun sear, not illustrated, is permitted to engage the sear notch 89 provided in portion 60 of the bolt block, the gun will continue to operate fully automatic, firing cartridge after cartridge until the supply has been exhausted. However, if it becomes necessary or desirable to operate the gun single shot, this may be done by permitting the gun sear to engage notch S9 for releasably maintaining or locking the parts in the relative positions disclosed in Fig. 3.

In Figs. 5 and 6, a modified form of adapter unit is disclosed, said unit comprising a lock frame 32| having a pair of spaced side walls 90 and 9|, a rear wall 92 and a forward lock frame block 53. The bolt block and hammer assembly disclosed in Fig. 7 is adapted to be inserted between walls 90 and 9|, said walls acting as guides for directing the reciprocation of the bolt and hammer. The primary distinction between the adapter disclosed in Figs. 5 and 6 and that disclosed in Figs. 2 to 4 inclusive resides in the modified form of cooking knob 020 and in the structural details of the means used to releasably maintain hammer 38 in a cocked position, and in the structural details of the means utilized for tripping the hammer as the bolt block is shot forwardly, to the right, by means of recoil spring 33. If desired a hammer spring guide 39 may be provided, as illustrated. With reference now to Figs. 6 and '1, it will be observed that hammer 39 includes a rearwardly projecting hammer limb or member 93 the free outer edge of which terminates in an upturned lip '99 which is adapted to be releasably engaged by a complementary depending latch member 95 of sear 9S pivotally mounted on a pivot pin 91 secured between and carried by walls 99 and 9|. The sear is normally urged in a clockwise direction about pivot pin 91 by means of spring 90. Sear y99 is adapted to be moved in a counterclockwise direction about pivot pin 91 for effecting a disengagement of latch member V from upturned lip 94 of hammer limb 93 by means of a sear trip member 99 mounted for reciprocatory motion on a track undercut in side wall 9| of lock frame 32|, see Figs. 9 and 10, which includes a ramp |00 which is complementary to inclined face |0| of depending leg |02 of the sear 9B, see Fig. 8. The sear trip member likewise includes a sto-p pin |03 at its rear end and a stop pin 200 at its front end, which pins are adapted to be engaged by bolt lug 66 of the bolt block as said bolt block reaches the end of its rearward and forward` strokes respectively. When the bolt block is shot forward- 1y, to the right, by the recoil spring 33, it strikes pin 200 thereby shifting the sear trip member 99 to the right for effecting engagement of ramp |00 with inclined face |0| for lifting latch member 95 thereby releasing the hammer to a ring position. As the bolt block moves rearwardly it will engage and move hammer 36 rearwardly to a retracted sear engaging position, and lug 66 will engage pin |03 for shifting the sear trip member 99 to the left. The numeral 20| indicates a notch into which a standard extractor unit may be int sear in hammer cocked and hammer released positions respectively.

lThe adapter disclosed in Fig. 11 embodies a rotary sear |04 in lieu of the pivoted sears disclosed in Figs. 2, 3, 4, 6, S, 9 and 10, With particular reference to Fig. 11, it will be observed that the rotary sear member .|04 includes a tubular portion |05 one end of which terminates in an enlarged collar member |09 which is provided with a tapered sear notch |01. Tubular portion |05 may be mounted for rotary motion around a shaft-like member |08 which may be formed as an integral part of the rear wall of the lock frame 32|, which comprises a pair of spaced side walls 900 and 9|0, and forward lock frame block 53. Shaft-like member |99 is preferably hollow to provide a spring receptive chamber |51 into which hammer spring 38 extends.

As disclosed in Fig. 12, hammer 30 includes a rearwardly extending arm or hammer branch |99 which terminates in an out-turned lip H9 which is adapted to engage the tapered sear notch |01. 4Scar |04 is adapted to be rocked or rotated about shaft |08 by means of a bolt abutment member provided on bolt block 3.| as illustrated. As disclosed in Figs. 13 and 14, collar member |00 is provided with a flattened cam follower surface H2 which is adapted to be engaged by bolt abutment member for rocking or rotating sear |04 about shaft |08. The Sear is normally urged in a counterclockwise direction by means of a spring |13, or the like, for positioning the tapered sear notch |01 to engage lip H0 of the hammer. -A spacer block 350 may be 1ocated between the rear wall of lock frame 32| and the rear wall of the receiver.

In operation, the hammer 36 will be retained in a retracted, cocked position by sear .|013 until such time as bolt abutment member i is caused to pass under flattened surface |2 for rotating the sear from the position disclosed in Fig. 13 to that disclosed in Fig. 14. It will be understoodv that the longitudinal path of bolt abutment mem ber is so related to sear |011 as to be disposed on one side or the other of a vertical through the center of shaft |88 to provide a rocking or rotating motion to the sear against the counterforce of spring H3 as the abutment member is caused to travel beneath flattened surface |2.

The adapter unit disclosed in Fig. l differs from that disclosed in Figs. 5 to 10 inclusive primarily in that bolt lug 66 is adapted to move longitudinally between a pair of spaced lugs M4 andY H5 provided at the front and rear ends of a sear trip member H6 which is mounted for limited longitudinal motion on pins which cooperate with elongated slots H8 provided in the body of the trip member. A ramp ||9 is provided as shown for cooperation with inclined face l2@ of sear |2|. Sear |2| is pivotally mounted about pivot pin |22, and is urged in a clockwise direction by means of spring |23 whereby Sear latch member `95 is normally urged to engage slot |212 of hammer 36.

It will be observed that a different type of insert barrel is disclosed in Fig. 1 than is disclosed in Figs. 2 to e inclusive. The insert barrel of Figs. 2 to l inclusive is what will hereinafter be referred to as a short insert barrel 3|, the end 5i of which terminates from the end 5.2 of the submachine gun barrel by a dimension indicated by the letter X. The short insert barrel, as has already been explained, is inserted into the larger calibre barrel of the gun from the rear thereof, and that portion of the regular gun barrel beyond the end of the insert barrel functions as an. auxiliary expansion chamber for imparting a lift or upward kick to the gun barrel each time a cartridge is fired.

In those instances where it is desirable to obtain maximum accuracy of .the .22 calibre projectile, the so-called long insert barrel |3| disclosed in Fig. 1 may be used. The forward end of the barrel may be provided with external threads |25 and the rear end may be provided with external threads 52e. The barrel is adapted to be inserted through the large calibre gun barrel from the front, being held in place by the threaded engagement of external threads |25 with complementary internal threads |21 provided at the forward end of an insert barrel stub |28 which may be formed as an integral part of the lock frame 32, or which may be provided in the forward edge of a separate sub-barrel insert piece 82 disclo-sed in Fig. l5, the overall length of which, denoted by the letter Z, corresponds with the length of the regular short insert barrel 3| disclosed in Figs. 2 4, measured from rear face |29 to shoulder |32. In those instances where the sub-barrel 82 is used, the same adapter unit may be employed for use with a short insert barrel 3| or a long insert barrel V3i.

With reference to Fig. l, it will be observed that external threads |25 are disposed beyond forward end 52 of the large calibre barrel 4l. Such an arrangement is desirable in order that an expansion chamber or nozzle |32 of the general type disclosed in Fig. 16 may be associated with a long insert barrel for emphasizing the recoil and barrel lift characteristics of the gun when it is operated on .22 calibre ammunition, and whereby such characteristics will approach those inherent when the gun is operated on .45 calibre ammunition.

The expansion nozzle may be provided with internal threads |33 which are adapted to engage threads |25 of the long insert barrel. An opening |36 is provided in the forward end of the nozzle, said opening being of a dimension sufcient to facilitate the passage of a .22 calibre projectile therethrough. The inner face |35 of .the nozzle between threads |33 and opening |34 is preferably tapered toward the opening as illustrated. If desired, a plurality of vent holes indicated by the numeral |36 may be provided for the purpose of permitting the hig-h pressure gases of combustion to be vented downwardly therethrough for effecting an upward reaction to the end of the gun.

Unlike ammunition of .45 calibre and larger in which the cartridge bases are of substantially the same diameter as the cartridge cases, the bases of .22 calibre rimre cartridges are appreciably larger in diameter than their respective casings, thereby rendering impractical those types of cartridge magazines customarily used with the larger calibre ammunition. When .22 calibre rimfire cartridges are stacked one upon another, they will assume the relationship disclosed in Fig. ll, wherein each succeedingly lower cartridge is disposed at a greater inclination than the one immediately preceding it. The forward edges |35 of projectiles 86 form an arc, when their bases or rims are disposed in contact with a vertical wall such as |31 of the magazine, said arc being directly proportional to the number of cartridges stacked. In order that each cartridge may be properly presented to stripping lips |22 and |32, a special cartridge feeding platform has been provided.

With reference to Figs. 17 and 18 it will be observed that magazine may comprise a pair of spaced rear and front walls |37 and Mil, a pair of spaced side walls lill and |42 and a bottom |63. The lateral distance between front and rear walls lll@ and |31 is of a dimension somewhat greater than the overall length of a .22 calibre cartridge, and the lateral distance between side walls |4| and |42 may be of a dimension somewhat larger than the diameter of base 65 of a cartridge, see Fig. 20. A follower M4 having such a contour and dimensions as to slidably engage front and rear walls Mill and |31 and side walls |4| and |42, may be provided. Suitable means such as a follower spring |l5 may be interposed between bottom wall |23 and the follower` for normally urging the follower upwardly toward the stripping lips. A platform |45 may be pivotally secured to follower M4 about pivot pin |41. The free outer edge |558 of the platform may be normally urged downwardly by means of a spring |49, the lowerV end of said spring being anchored to follower fll, by any appropriate means. A vertical guide edge |52 which conforms in contour with the arc described by the forward edges |36 of projectiles te may be provided in one or both of side walls iihand |22. A follower pin |5| is carried by platform H56, said pin being rigidly secured to the platform and adapted to abut against arcuate guide edge |5il. It will be observed that as .follower lill; moves upwardly under the inuence of spring |45, platform |46 will be moved in a clockwise direction about pivot pin |41, as said platform approaches a horizontal plane. The angle of inclination of the platform is at all times dependent upon the relative location of follower UM, whereby the angle of lift of platform |136 will automatically be adjusted to compensate for the inclination of the cartridges as theyare intermittently presented to the stripping lips. In this manner it is possible to effectively feed .22 calibre rimre cartridges at a rate of speed sufficient to permit a sub-machine gun to operate at cyclic rates up to 800 shots per minute, without jamming the cartridges. If desired, a lug |52 may be formed integrally with follower ld, and projected outwardly through a vertical slot |53 provided in rear wall i3?. Lug |52 is adapted to operate a device provided on most regular .45 calibre sub-machine guns for the purpose of locking the bolt in an open position after the last cartridge of the magazine has been fired. A pair of outwardly projecting finger grip members |54 and |55 may be secured t0 follower H34 for enabling the follower to be retracted against the counterforce of spring M during the insertion of ammunition into the magazine,

Stripping lips |38 and |39 are designed to resiliently retain the uppermost cartridge in alignment with stripping lug 2 of bolt 5S, whereby the uppermost cartridge cannot be accidentally or unintentionally dislodged from the magazine. In Fig. the parts are shown in position as the bolt is moving backward, to the left, in recoil, it being understood that as soon as stripping lug l2 is moved back far enough to clear cartridge base or rim 55 that the uppermost cartridge will be lifted vertically by spring |55 whereby the stripping lips will engage the cartridge case 85. When thus engaged rim E5 projects a substantial distance above the upper edge of stripping fingers |38 and |39 and in line with stripping lug 42 of the bolt. An ejector 8S may be suitably secured to side wall |62 of the magazine, said ejector including a cartridge base engaging finger |55 against which the rear face of a cartridge base is adapted to strike incident to the rearward travel of an empty cartridge case by the back pressure generated incident to the firing of a cartridge, as has already been explained.

It should be understood that the upper portion of magazine l is adapted to be inserted upwardly through an opening provided in the lower wall of the chamber e9 of the insert barrels, whereby cartridges may be fed directly from the stripping lips of the magazine into the rear end of an insert barrel. The regular .45 cartridge ramp, indicated in Figs. 1 to 4 inclusive by the numeral |58, is not used.

The magazine may be secured to the gun frame in the same manner and using the same magazine mounting means as are used when a regular large calibre ammunition magazine is mounted to the gun frame.

It should be understood that the frame includes a hand grip portion Sill, a trigger 3M, a suitable trigger mechanism, not illustrated, located in housing SBS, see Fig. l. Trigger 3&2 may be utilized for actuating a Sear not shown, which may engage sear notch 8g of the rearward eX- tending boli-I block 6d for controlling the firing cycle on the gun.

In those instances where the large calibre regular barrel di of a machine gun is provided with a Cutts compensator device, the effect of such a device may be nullied by using a long insert barrel, such as |S|, the length of which is of such a dimension as to locate the externally threaded portion |25 beyond the end of the Cutts compensator, whereby the effect of the compensator will be nullied and an expansion chamber |32 may be mounted on-the insert barrel for exaggerating the recoil and barrel lift characteristics of the gun.

It should be understood th'at various modications and changes in the structural details of the device may be made, such as making spacer block 35 an integral part of the lock frame, within the scope of the appended claims, without departing from the spirit of the invention.

I claim:

l. In an automatic firearm, a breech chamber, a bolt block positioned in and mounted for reciprocation longitudinally of said chamber, a hammer mounted for reciprocation on and longitudinally of said bolt block, means to guide said bolt block and hammer during their reciprocatory movements, resilient means normally urging said bolt block and said hammer toward a forward projected position, said hammer provided with a rearwardly extending limb terminating in a catch member, a bearing shaft in and extending longitudinally of the breech chamber, a sear rotatably mounted on said bearing shaft, said sear being positioned above the bolt block and provided with a latch member for releasably engaging said hammer limb catch member, resilient means normally rotating and holding said sear to a catch engaging position in respect to said hammer limb catch member, a cam folltwer on said sear, means carried by the boli; block constructed and arranged to engage said cam follower as th'e bolt block` approaches a forward projected position, and said last named bolt block carried means operating to rotate said sear and release the latch member thereof from engagement with the catch member of the hammer limb.

2. In an automatic firearm, a breech chamber, a bolt block positioned in and mounted for reciprocation longitudinally of said chamber, a hammer mounted for reciprocation on and longitudinally of said bolt block, means to guide said bolt block and hammer during their reciprocatory movements, resilient means normally urging said bolt block and said hammer toward a forward projected position, said hammer provided with a rearwardly extending limb terminating in a catch' member, a bearing shaft in and extending longitudinally of the breech chamber, a tubular sear rotatably mounted on said bearing shaft, said sear including an annular collar having a cut-out portion providing o, latch member constructed and arranged to releasably engage said hammer limb catch member, resilient means normally rotating and holding said sear to a catch engaging position in respect to said hammer limb catch member, a cam surface on said sear collar, means carried by the bolt block constructed and arranged to engage said sear collar cam surface as the bolt block approachesl a forward projected position, and said last named bolt block carried means operating to rotate said sear and release the latch member thereof from engagement with the catch member of the khammer limb.

3. A construction as dened in claim 2 wherein, the resilient means normally urging the hammer toward a forward projected position extends from the hammer to and in engagement with an abutment at the rear end of the breech chamber, and said sear bearing shaft being hollow for the passage oi said resilient means therethrough,

4. In an automatic rearm, a breech chamber, a bolt block positioned in and mounted for reciprocation longitudinally of said chamber, a hammer mounted for reciprocation on and longitudinally of said bolt block, means to guide said bolt block and hammer during their reciprocatory movements, resilient means normally urging said bolt block and said hammer toward a forward projected position, said hammer provided with a 1 1 rearwardly extending limb terminating in a catch member, aV bearing shaft in and extending `longitudinally of the breech ch'amber, a Ysear rotatably mounted on said bearing shaft, said sear having a collar-like portion extending transverse said breech chamber and provided with a cut-out portion for the passage of the hammer limb and its( catch member to provide a latch for releasably. engaging said hammer limb catch member, resilient means normally rotating and holding said sear to a catch engaging position in respect to` said hammer limb catch member, one face of the. cut-out portion of said sear collar-like member being beveled and said hammer limb provided with a beveled portion constructed and arranged to engage the beveled portion of the Sear to Cause rotation of the Sear to permit the passage therethrough of the hammer limb and its catch member when the hammer is moved to a retracted position, a cam surface on said sear, means carried by the bolt block constructed and arranged to engage said sear cam surface as the bolt block approaches a forward projected position,I and said last named bolt block carried means operating to rotate said Sear and release the catch member thereof from engagement with the catch member of the. hammerlimb.

CHARLES WILLIAM ROBBINS.

1 2 REEEBENCES. orrEl The following references are ofl record Vin the lc of this patent:

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